Differential drive spiral accumulator apparatus

ABSTRACT

Various designs of a spiral accumulator apparatus are disclosed for controlling the flow of articles. The accumulator may have an infeed conveyor driven in a first direction to convey articles therealong in the first direction along a first path that is at least partially curved, and an outfeed conveyor driven in an opposite direction to convey articles therealong in the opposite direction along a second path that is at least partially curved. The infeed and outfeed conveyors may be spaced apart and generally parallel along at least a portion of the first and second paths so as to define a space therebetween. A movable transport member may be disposed generally across and movable along the space, and an article transfer member may be carried by the transport member and operably disposed between the infeed and outfeed conveyors to transfer articles between the infeed conveyor and the outfeed conveyor. A transport member mover may be connected to the transport member. A differential drive mechanism may be located at a fixed position spaced from the transport member, the differential drive mechanism including an output portion for contacting and moving the transport member mover when a relative speed difference exists between the infeed and outfeed conveyors thereby causing the transport member to travel in the direction of the faster of the infeed and outfeed conveyors. The differential drive mechanism may include a plurality of gears, or it may include condition responsive devices and related motors and controls, for driving the transport member mover.

FIELD OF THE INVENTION

The present invention relates generally to a spiral accumulatorapparatus for controlling the flow of articles from an upstream deliverystation to a downstream receiving station using a differential drive;and more particularly to an apparatus including an article transfermember moved via a remote differential drive mechanism.

BACKGROUND OF THE INVENTION

Accumulators have been utilized between an upstream delivery station anda downstream receiving station to accumulate articles when the capacityof the downstream receiving station is either shut down or run at aspeed wherein it cannot handle the number of articles being fed by theupstream delivery station. One particular accumulator is disclosed inU.S. Pat. No. 4,018,325. One problem with such accumulators is that thelast article fed into the accumulator is the first article fed out ofthe accumulator and, as a result, it is difficult to keep track of thebatch from which a particular article came from, and the sequence inwhich the articles are fed from the upstream delivery station.

Accumulators have been made wherein the first article in is the firstarticle out. Such “first in, first out” accumulators are sometimes knownas “FIFO” accumulators. For example, the owner of the presentapplication is also owner of U.S. Pat. Nos. 6,152,291, 6,182,812,6,230,874, 6,260,688, 6,382,398, 6,497,321, 6,523,669, 6,533,103,6,550,602, 6,585,104, and 6,612,420, all disclosing various aspects ofFIFO conveyors, and all incorporated by references herein for allpurposes.

Various of the above patents disclose accumulators having conveyorsextending along multi-level curved paths, with a transfer mechanismdisposed between the conveyors for transferring the conveyed objectsbetween the conveyors. Such accumulators are commonly called spiralaccumulators. As disclosed, the transfer mechanisms of such spiralaccumulators may be driven by rotatable members which contact theoppositely moving conveyors (or attachments thereto) at the point oftransfer. The rotatable members travel with the transfer mechanism alongthe conveyors, at a position dictated by the relative speeds of theconveyors.

SUMMARY OF THE INVENTION

According to some aspects of the invention, a spiral accumulatorapparatus is disclosed for controlling the flow of articles. Theaccumulator includes a support structure, an infeed conveyor mounted tothe support structure and driven in a first direction to convey articlestherealong in the first direction along a first path that is at leastpartially curved, and an outfeed conveyor mounted to the supportstructure and driven in an opposite direction to convey articlestherealong in the opposite direction along a second path that is atleast partially curved. The infeed and outfeed conveyors are spacedapart and generally parallel along at least a portion of the first andsecond paths so as to define a space therebetween. A track is mounted tothe support structure along at least a portion of the space, and amovable transport member is disposed generally across and movable alongthe space on the track. An article transfer member is carried by thetransport member and operably disposed between the infeed and outfeedconveyors to transfer articles between the infeed conveyor and theoutfeed conveyor. A transport member mover is connected to the transportmember, the transport member mover including an endless loop. Adifferential drive mechanism is located at a fixed position spaced fromthe transport member. The differential drive mechanism includes anoutput portion for contacting and moving the transport member mover whena relative speed difference exists between the infeed and outfeedconveyors thereby causing the transport member to travel in thedirection of the faster of the infeed and outfeed conveyors. Variousoptions and alternatives are also available.

For example, if desired, the endless loop may be a belt, a cable, or anyequivalent. The differential drive mechanism may include a plurality ofgears. If so, the plurality of gears may include two input gears and adifferential gear, one of the input gears being attached to an axlerotating at a speed related to that of the infeed conveyor and the otherof the input gears being attached to an axle rotating at a speed relatedto that of the outfeed conveyor, the differential gear being driven bythe two input gears so as to drive the output portion of thedifferential drive mechanism.

The differential drive mechanism may be operatively interconnected withaxles driven by the infeed and outfeed conveyors. Also, the differentialdrive mechanism may include condition responsive devices for detectingdirectly or indirectly a speed of the infeed and outfeed conveyors, amotor, and a drive control for driving the motor based on the speeds ofthe infeed and outfeed conveyors so as to move the output portion of thedifferential drive mechanism at a desired speed.

Guide members may be mounted to the support structure for guiding thetransport member mover, and the guide members may include geared orgrooved pulleys and/or idler rollers.

The differential drive mechanism may drive the transport member mover ata speed equal to half the difference between the speeds of the infeedand outfeed conveyors. Also, the differential drive mechanism may drivethe transport member mover at a speed proportional to as₁−bs₂, where s₁is the speed of the infeed conveyor and s₂ is the speed of the outfeedconveyor, and a and b are adjustable parameters.

According to certain other aspects of the invention, a spiralaccumulator apparatus is disclosed for controlling the flow of articles.The accumulator includes an infeed conveyor driven in a first directionto convey articles therealong in the first direction along a first paththat is at least partially curved, and an outfeed conveyor driven in anopposite direction to convey articles therealong in the oppositedirection along a second path that is at least partially curved. Theinfeed and outfeed conveyors are spaced apart and generally parallelalong at least a portion of the first and second paths so as to define aspace therebetween, and a movable transport member is disposed generallyacross and movable along the space. An article transfer member iscarried by the transport member and operably disposed between the infeedand outfeed conveyors to transfer articles between the infeed conveyorand the outfeed conveyor, and a transport member mover is connected tothe transport member. A differential drive mechanism is located at afixed position spaced from the transport member, the differential drivemechanism including an output portion for contacting and moving thetransport member mover when a relative speed difference exists betweenthe infeed and outfeed conveyors thereby causing the transport member totravel in the direction of the faster of the infeed and outfeedconveyors. Various further options and alternatives are also possiblewith this accumulator, as above.

According to another aspect of the invention, a spiral accumulatorapparatus for controlling the flow of articles is disclosed. Theaccumulator includes an infeed conveyor driven in a first direction toconvey articles therealong in the first direction along a first paththat is at least partially curved, and an outfeed conveyor driven in anopposite direction to convey articles therealong in the oppositedirection along a second path that is at least partially curved. Theinfeed and outfeed conveyors are spaced apart and generally parallelalong at least a portion of the first and second paths so as to define aspace therebetween. A movable transport member is disposed generallyacross and movable along the space, and an article transfer member iscarried by the transport member and operably disposed between the infeedand outfeed conveyors to transfer articles between the infeed conveyorand the outfeed conveyor. A transport member mover is connected to thetransport member. A differential drive mechanism is located at a fixedposition spaced from the transport member. The differential drivemechanism includes two input gears and a differential gear, one of theinput gears being attached to an axle rotating at a speed related tothat of the infeed conveyor and the other of the input gears beingattached to an axle rotating at a speed related to that of the outfeedconveyor, the differential gear being driven by the two input gears soas to drive an output portion of the differential drive mechanism. Theoutput portion contacts and moves the transport member mover when arelative speed difference exists between the infeed and outfeedconveyors thereby causing the transport member to travel in thedirection of the faster of the infeed and outfeed conveyors. Again,various options and modifications are possible with this accumulator, asabove.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view illustrating an apparatus for controlling the flowof articles in its basic form.

FIG. 2 is a plan view of the apparatus of FIG. 1 showing articles beingloaded into the apparatus.

FIG. 3 is a plan view of a modified form of the design of FIG. 1.

FIG. 4 is a schematic diagram illustrating an apparatus storing articlesin a vertical spiral.

FIG. 5 is a perspective view of a transport member mounted on a trackand attached to a transport member mover according to certain aspects ofthe invention.

FIG. 6 is a perspective view of a differential drive mechanism accordingto certain aspects of the present invention.

FIG. 7 is a partially exploded perspective view of the differentialdrive mechanism of FIG. 6.

FIG. 8 is a perspective view of an alternate differential drivemechanism as in claim 6, but with cable and pulley.

FIG. 9 is a schematic diagram of an alternate differential drivemechanism according to certain aspects of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 1-4, there is broadly illustrated an apparatus 10 forcontrolling the flow of articles A from an upstream delivery station to12 a downstream receiving station 14. The articles are carried on a mainconveyor 16 that is driven by any conventional conveyor drive mechanism.The articles are fed along the main feed conveyor 16 until they reachapparatus 10, at which point they exit conveyor 16 and enter apparatus10. Eventually, the articles are returned to main conveyor 16 in a FIFOsequence.

Apparatus 10 includes a support structure 18 that, as shown, may includevarious vertical members 20 and horizontal members 22. The layout ofsupport structure 18 may take any desired form depending on the size ofand application for apparatus 10. Thus, support structure 18 shownherein is merely an example, and any modifications to that shown shouldbe considered as within the scope of the present invention. FIGS. 1-3show only vertical members 20 of support structure for clarity.

Apparatus 10 includes a deflecting rail 24 for deflecting articles A offthe main conveyor 16 onto an infeed conveyor 26 carried on supportstructure 18. Infeed conveyor 26 is an endless conveyor and is driven byan infeed drive mechanism 28, which may include a variable speed motor30 and a motor control 32.

An outfeed conveyor 34 is also carried on support structure 18. Asubstantial portion of the runs of the infeed and outfeed conveyors 26and 34 are parallel to each other providing a space 36 therebetween. Anoutfeed drive mechanism 42, which may include a variable speed motor 44and a motor control 46, drives the outfeed conveyor 34. A deflectingrail 24 is also located so as to deflect articles off outfeed conveyor34 back onto main conveyor 16.

A transport member 38 rides on a track 40 carried by support structure18 that permits the transport member to move backwards and forwardsalong the length of the infeed and outfeed conveyors 26 and 34. Infeeddrive mechanism 28 drives infeed conveyor 26 in a first direction on oneside of track 40, and outfeed drive mechanism 42 drives outfeed conveyor34 in a second direction on the other side of the track.

A transport member mover 48 is operably connected to the transportmember 38 and is driven by a differential drive mechanism 50. Thetransport member mover 48 may comprise an endless loop such as a belt,chain, cable, or the like, that rides in or along track 40. If desired,guide members 41 such as geared or grooved pulleys or idler rollers maybe utilized to guide transport member mover 48.

Differential drive mechanism 50 is mounted to support structure 18 andis operatively engaged with infeed and outfeed conveyors 26 and 34. Aswill be discussed below in greater detail, differential drive mechanismincludes two axles 52 and 54 joined at a differential housing 56. Axles52 and 54 rotate respectively with infeed and outfeed conveyors 26 and34, as a function of the speed of the conveyors. As shown, axles 52 and54 are driven directly by contact with conveyors 26 and 34 via rollers53 and 55. However, it would also be possible to obtain input rotationspeed information from other idler or driven members, rotated byconveyors or motors, both directly or indirectly, if desired. Transportmember mover 48 rotates around an output portion of housing 56 as thehousing moves, dependent on the differential speeds of shafts 52 and 54,based ultimately on the conveyor speeds (see FIGS. 6-8). Accordingly,transport member 38 is driven relative to conveyors 26 and 34 along apath parallel to the conveyors, at a speed and direction depending onthe relative speed of the conveyors. An article transfer member 58 iscarried by transport member 38 for deflecting articles from infeedconveyor 26 to outfeed conveyor 34.

The speeds of the conveyors 26 and 34 are controlled by drive mechanisms28 and 42. If the speed of outfeed conveyor 34 is slower than the speedof infeed conveyor 36, then transport member 38 is moved in thecounter-clockwise direction (as shown in FIGS. 1-3), thereby increasingthe number of articles on the surfaces of the infeed conveyor and theoutfeed conveyor for temporarily storing the articles in the accumulator10. If the speed of outfeed conveyor 34 is greater than the speed ofinfeed conveyor 26, transport member 38 will move in a clockwisedirection (as shown in FIGS. 1-3), thereby reducing the number ofarticles stored on the infeed and outfeed conveyors, with FIFOsequencing.

Condition responsive devices may be positioned along the conveyors forgenerating signals responsive to various conditions. For example, acondition responsive device 60 may be positioned adjacent to mainconveyor 16 for sensing a backup of articles on the main conveyor; andif such a condition occurs a signal may be sent to a motor control 32which causes the motor 30 to shift to a higher speed, thereby speedingup infeed conveyor 26. The condition responsive device 60 may be anysuitable conventional sensor, but in one particular embodiment it is aphotocell provided with a timer so that if the photocell is activatedfor a certain period of time by non-movement of the article a signal isgenerated. The articles A carried on the main conveyor are spaced apart,and as long as the space is sensed between the articles in a givenperiod of time then no signal is generated by the photocell to triggeran increase in speed of the infeed conveyor 26. One suitable photocellis manufactured by Sick A.G. having a part number of WT4-2P135S10. SickA.G. is located in Wldkirch, Germany. It is to be understood that anyconventional suitable condition responsive device could be used at anyof the locations where one is required.

Another condition responsive device 62 may be positioned along mainconveyor 16 closely adjacent to the front end of the rail 24. Thisdevice is provided to sense a backup on conveyor 16, and causes a signalto be produced to reduce the speed of conveyor 16 to a medium speed.Another condition responsive device 64 may be positioned near theentrance of infeed conveyor 26 for sensing a lack of articles on theinfeed conveyor. This sensor generates a signal to the stop the infeedconveyor when such a condition occurs.

There may be still another condition responsive device 66, positionedadjacent to main conveyor 16, where the articles are fed back onto themain conveyor. When a backup of articles is sensed by conditionresponsive device 66 on the main conveyor 16, a signal is sent to motorcontrol 46 to stop the outfeed conveyor 34. A backup is sensed when thearticles exiting off of outfeed conveyor 34 are pressed against eachother on main conveyor 16.

Under normal operation, main conveyor 16 is running at a higher speedthan outfeed conveyor 34, and as the articles are transferred from theoutfeed conveyor onto the main conveyor a space is developed between thearticles. Condition responsive device 66 is thus provided for ensuringthat this space remains between the articles, and if the space is lostas a result of a backup of articles then the outfeed conveyor 34 isstopped.

A still further condition responsive device 68 may be positioned furtherdown the line on main conveyor 16, and when it senses that there is nospace between articles being delivered back onto the main conveyor asignal is generated, which is fed to variable motor control 46 foroutfeed conveyor 34, for reducing the speed of variable speed motor 44.

All of the signals generated by condition responsive devices 60-68 arefed to motor controllers 32 and 46 (or the controller for conveyor 16,not shown), which may comprise conventional controllers such as aprogrammable logic controller. One suitable programmable logicalcontroller is manufactured by Allen Bradley and has a model number ofSLC500 series. Allen Bradley is located in Milwaukee, Wis. Othercontrollers may also be utilized within the scope of the invention.

In order for transport member 38 to move from the position shown in FIG.2 to the position shown in FIG. 1 the speed of infeed conveyor 26 mustbe running faster than the speed of outfeed conveyor 34. As a result,when transport member 38 is moved in a counter-clockwise direction it isloading articles from infeed conveyor 26 to outfeed conveyor 34 forstoring the articles. As previously mentioned when the demand at thedownstream receiving station increases then the speed of outfeedconveyor 34 will increase over the speed of infeed conveyor 26 viatransport member mover 48, and the transport member will move in aclockwise direction from the position shown in FIG. 1 to the positionshown in FIG. 2 to unload the articles stored in the accumulator. Theconfiguration for the parallel run of infeed conveyor 26 and the outfeedconveyor 34 can vary depending on the amount of floor space that isdesired to be utilized for the accumulator. In FIGS. 1 and 2 theconfiguration of the infeed and outfeed conveyors is in a spiral. InFIG. 3 the configuration of infeed conveyor 26 and outfeed conveyor 34is also in a spiral but it has an elongated middle portion. If there issufficient floor space the run of the two conveyors can be in ahorizontal plane.

As shown in FIG. 4 the configuration of infeed conveyor 26 and outfeedconveyor 34 is in a vertical spiral so that a substantial amount ofstorage can be placed in a relatively small space. Sometimes as theheight of the spiral increases it is necessary to additionally drive theinfeed and outfeed conveyors along the vertical path of the spiral so asto minimize the drag of the conveyors on the track. The additional drivemechanism is shown in schematic form in FIG. 4.

As can be seen in FIG. 4 infeed conveyor 26 and outfeed conveyor 34 areendless conveyors. Infeed conveyor 26 is driven by motor 30, and itspath extends upwards from adjacent main conveyor 16 in a spiralconfiguration to pass over a drive sprocket 70 then down a vertical runthrough an idle sprocket 72 and back to the track which holds theconveyor in a vertical spiral. The track (not shown) for holding theconveyor may be of any suitable construction and is supported onvertical members 20 and horizontal members 22. Outfeed conveyor 34 isdriven by outfeed drive motor 44 by means of drive sprocket 74. Theconveyor belt 34 passes around idle sprockets 76 and 78 in its run.Infeed conveyor 26 and outfeed conveyor 34 may be constructed of anysuitable conventional chain belt that has connecting links 80, and inone particular embodiment has an upper surface such as shown in FIG. 5.

One example of a gear-based differential drive mechanism useful with thespiral accumulator designs disclosed above is shown in more detail inFIGS. 6 and 7. As shown, the mechanism includes four bevel gears 82 A-D.The outfeed axle 52, rotating (as shown) at the speed of the outfeedconveyor 34 (not shown, but traveling around rollers 53), is connectedto the bevel gear 82A. The infeed axle 54, rotating (as shown) at thespeed of infeed conveyor 26 (not shown, but traveling around rollers55), is connected to opposite bevel gear 82B. The gears mesh with gears82C and 82D, which are coaxially and rotatably aligned as pinion gearson pinion shaft 84. Couplings 86 retain the bevel gears in place on theaxles and pinion shaft. The ends of pinion shaft 84 extend from a spider88, which also provides supports for axles 52, 54. The differentialmechanism fits in a hollow 90 formed in the center of two mating centralhousing halves 92. The ends of pinion shaft 84 fit in cavities 94 formedradially in the housing halves. Metal plates 96 serve as thrustbearings. Dowels 98 register the two housing halves, which are heldtogether conventionally by bolts or screws through holes 100. A toothedsprocket wheel 102 is attached to each housing half. The peripheralteeth of the sprocket wheel engage a driven belt, comprising thetransport member mover 48, to drive it.

The geared differential works conventionally in that relative motion ofshaft output bevel gears 82A and 82B causes pinion gears 82C and 82D torotate about the axis of axles 52, 54. As the pinion gears rotate, theends of pinion shaft 84 cause housing 56 and sprocket wheels 102 torotate. The speed of rotation depends on the relative speeds of therotation of the output shaft bevel gears. In the situation where theoutfeed conveyor and the infeed conveyor are moving at the same speed inopposite directions, outfeed output bevel gear 82A rotates in onedirection at a certain speed and the infeed output bevel gear 82Brotates in the opposite direction at the same speed, which causes thepinion gear assembly to rest with its pinion shaft stationary. As one ofthe conveyors 26 or 34 speeds up relative to the other, differentialdrive mechanism 50 causes the housing and sprocket wheel assembly torotate in the direction of the faster moving rotating assembly, but athalf the difference between the speeds of each rotating assembly. Thus,in this example, the speed s of transport member mover 48 is given by:S=½ (s₁−s₂), where s₁ is the speed of the faster-moving belt and s₂ isthe speed of the slower-moving conveyor. Of course, the gearing ratioscan be altered by the use of gear reducers or other conventionaltechniques to derive other speed relationships that maybe genericallydefined by s is proportional to as₁−bs₂, where a and b are parametersset by the effective gear ratios, for example. This would allow thetransport member mover to be driven at a speed that is influencedrelatively more by one of the conveyors than the other in specialapplications. Also, the ratios could be changed if the widths of theconveyors were not equal, which could be desirable in some situations.

As shown in FIG. 8, it would be possible to modify transport membermover 48′, for example by substituting a cable for the illustrated belt.If so, members 41 could be a pulley or the like, and guide track 40would have to also be modified accordingly. Also, housing 56 wouldlikely be modified as well, so that the output portion driving transportmember mover 48′ would not necessarily be two, toothed sprocket wheels,but would comprise a groove 102′ for receiving the cable. Various othermodifications would also be possible to transfer differential rotationalmotion from a differential housing to transport member mover. It shouldbe understood that all such modifications and options are considered tobe within the scope of the invention.

Another example of a differential drive mechanism useful with the abovespiral accumulators is shown diagrammatically in FIG. 9. As shown,differential drive 50′ includes a housing 56′ disposed between conveyors26 and 34 for driving transport member mover 48. As shown, transportmember mover 48 is a cable but, as above other structures could be usedwith suitable corresponding modifications. Condition responsive devicessuch as an infeed conveyor speed sensor 104 and an outfeed conveyorspeed sensor 106 are also provided. As shown schematically in FIG. 9,sensors 104 and 106 may measure the rotational speed of axles 52 and 54directly, or in another way such as via related rotational axles or viadifferential housing 56′. Accordingly, sensors 104 and 106 may compriseoptical or mechanical transducers or the like. Alternatively, sensors104 and 106 could directly measure the speed of conveyors 26 or 34.Sensors 104 and 106 are in communication with a motor controller 108that drives a motor 110 depending on the sensed speeds. Controller 108can use logic, along the lines described above, to determine an outputspeed and direction for housing 56′ and can drive motor 110 accordingly.Controller 108 may be a programmable logic controller, as describedabove.

While preferred embodiments of the invention have been described above,it is to be understood that any and all equivalent realizations of thepresent invention are included within the scope and spirit thereof.Thus, the embodiments depicted are presented by way of example only andare not intended as limitations upon the present invention. Whileparticular embodiments of the invention have been described and shown,it will be understood by those of ordinary skill in this art that thepresent invention is not limited thereto since many modifications can bemade. Therefore, it is contemplated that any and all such embodimentsare included in the present invention as may fall within the literal orequivalent scope of the appended claims.

1. A spiral accumulator apparatus for controlling the flow of articles,comprising: a support structure; an infeed conveyor mounted to thesupport structure and driven in a first direction to convey articlestherealong in the first direction along a first path that is at leastpartially curved; an outfeed conveyor mounted to the support structureand driven in an opposite direction to convey articles therealong in theopposite direction along a second path that is at least partiallycurved; the infeed and outfeed conveyors being spaced apart andgenerally parallel along at least a portion of the first and secondpaths so as to define a space therebetween; a track mounted to thesupport structure along at least a portion of the space; a movabletransport member disposed generally across and movable along the spaceon the track; an article transfer member carried by the transport memberand operably disposed between the infeed and outfeed conveyors totransfer articles between the infeed conveyor and the outfeed conveyor;a transport member mover connected to the transport member, thetransport member mover including an endless loop; and a differentialdrive mechanism located at a fixed position spaced from the transportmember, the differential drive mechanism including an output portion forcontacting and moving the transport member mover when a relative speeddifference exists between the infeed and outfeed conveyors therebycausing the transport member to travel in the direction of the faster ofthe infeed and outfeed conveyors.
 2. The apparatus of claim 1, whereinthe endless loop is a belt.
 3. The apparatus of claim 1, wherein theendless loop is a cable.
 4. The apparatus of claim 1, wherein thedifferential drive mechanism includes a plurality of gears.
 5. Theapparatus of claim 4, wherein the plurality of gears includes two inputgears and a differential gear, one of the input gears being attached toan axle rotating at a speed related to that of the infeed conveyor andthe other of the input gears being attached to an axle rotating at aspeed related to that of the outfeed conveyor, the differential gearbeing driven by the two input gears so as to drive the output portion ofthe differential drive mechanism.
 6. The apparatus of claim 1, whereinthe differential drive mechanism is operatively interconnected withaxles driven by the infeed and outfeed conveyors.
 7. The apparatus ofclaim 1, wherein the differential drive mechanism includes conditionresponsive devices for detecting directly or indirectly a speed of theinfeed and outfeed conveyors, a motor, and a drive control for drivingthe motor based on the speeds of the infeed and outfeed conveyors so asto move the output portion of the differential drive mechanism at adesired speed.
 8. The apparatus of claim 1, further including guidemembers mounted to the support structure for guiding the transportmember mover.
 9. The apparatus of claim 8, wherein the guide membersinclude one of pulleys or idler rollers.
 10. The apparatus of claim 1,wherein the differential drive mechanism drives the transport membermover at a speed equal to half the difference between the speeds of theinfeed and outfeed conveyors.
 11. The apparatus of claim 1, wherein thedifferential drive mechanism drives the transport member mover at aspeed proportional to as₁−bs₂, where s₁ is the speed of the infeedconveyor and s₂ is the speed of the outfeed conveyor, and a and b areadjustable parameters.
 12. The apparatus of claim 1, wherein the infeedand outfeed conveyors are configured to convey the articles in a firstin, first out sequence.
 13. The apparatus of claim 12, wherein theinfeed and outfeed conveyors are configured to convey the articles in asingle file orientation.
 14. The apparatus of claim 12, wherein theinfeed and outfeed conveyors are configured to convey the articles in agreater than single file orientation.
 15. A spiral accumulator apparatusfor controlling the flow of articles, comprising: an infeed conveyordriven in a first direction to convey articles therealong in the firstdirection along a first path that is at least partially curved; anoutfeed conveyor driven in an opposite direction to convey articlestherealong in the opposite direction along a second path that is atleast partially curved; the infeed and outfeed conveyors being spacedapart and generally parallel along at least a portion of the first andsecond paths so as to define a space therebetween; a movable transportmember disposed generally across and movable along the space; an articletransfer member carried by the transport member and operably disposedbetween the infeed and outfeed conveyors to transfer articles betweenthe infeed conveyor and the outfeed conveyor; a transport member moverconnected to the transport member; and a differential drive mechanismlocated at a fixed position spaced from the transport member, thedifferential drive mechanism including an output portion for contactingand moving the transport member mover when a relative speed differenceexists between the infeed and outfeed conveyors thereby causing thetransport member to travel in the direction of the faster of the infeedand outfeed conveyors.
 16. The apparatus of claim 15, wherein thetransport member mover is an endless loop.
 17. The apparatus of claim16, wherein the endless loop is a belt.
 18. The apparatus of claim 16,wherein the endless loop is a cable.
 19. The apparatus of claim 15,wherein the differential drive mechanism includes a plurality of gears.20. The apparatus of claim 19, wherein the plurality of gears includestwo input gears and a differential gear, one of the input gears beingattached to an axle rotating at a speed related to that of the infeedconveyor and the other of the input gears being attached to an axlerotating at a speed related to that of the outfeed conveyor, thedifferential gear being driven by the two input gears so as to drive theoutput portion of the differential drive mechanism.
 21. The apparatus ofclaim 15, wherein the differential drive mechanism is operativelyinterconnected with axles driven by the infeed and outfeed conveyors.22. The apparatus of claim 15, wherein the differential drive mechanismincludes condition responsive devices for detecting directly orindirectly a speed of the infeed and outfeed conveyors, a motor, and adrive control for driving the motor based on the speeds of the infeedand outfeed conveyors so as to move the output portion of thedifferential drive mechanism at a desired speed.
 23. The apparatus ofclaim 15, further including a support structure, the infeed and outfeedconveyors being mounted to the support structure, and further includinga track mounted to the support structure and located at least partiallyin the space between the infeed and outfeed conveyors, the transportmember being movable along the track.
 24. The apparatus of claim 23,further including guide members mounted to the support structure forguiding the transport member mover.
 25. The apparatus of claim 23,wherein the guide members include one of pulleys or idler rollers. 26.The apparatus of claim 15, wherein the differential drive mechanismdrives the transport member mover at a speed equal to half thedifference between the speeds of the infeed and outfeed conveyors. 27.The apparatus of claim 15, wherein the differential drive mechanismdrives the transport member mover at a speed proportional to as₁−bs₂,where s₁ is the speed of the infeed conveyor and s₂ is the speed of theoutfeed conveyor, and a and b are adjustable parameters.
 28. Theapparatus of claim 15, wherein the infeed and outfeed conveyors areconfigured to convey the articles in a first in, first out sequence. 29.The apparatus of claim 28, wherein the infeed and outfeed conveyors areconfigured to convey the articles in a single file orientation.
 30. Theapparatus of claim 28, wherein the infeed and outfeed conveyors areconfigured to convey the articles in a greater than single fileorientation.
 31. A spiral accumulator apparatus for controlling the flowof articles, comprising: an infeed conveyor driven in a first directionto convey articles therealong in the first direction along a first paththat is at least partially curved; an outfeed conveyor driven in anopposite direction to convey articles therealong in the oppositedirection along a second path that is at least partially curved; theinfeed and outfeed conveyors being spaced apart and generally parallelalong at least a portion of the first and second paths so as to define aspace therebetween; a movable transport member disposed generally acrossand movable along the space; an article transfer member carried by thetransport member and operably disposed between the infeed and outfeedconveyors to transfer articles between the infeed conveyor and theoutfeed conveyor; a transport member mover connected to the transportmember; and a differential drive mechanism located at a fixed positionspaced from the transport member, wherein the differential drivemechanism includes two input gears and a differential gear, one of theinput gears being attached to an axle rotating at a speed related tothat of the infeed conveyor and the other of the input gears beingattached to an axle rotating at a speed related to that of the outfeedconveyor, the differential gear being driven by the two input gears soas to drive an output portion of the differential drive mechanism, theoutput portion contacting and moving the transport member mover when arelative speed difference exists between the infeed and outfeedconveyors thereby causing the transport member to travel in thedirection of the faster of the infeed and outfeed conveyors.
 32. Theapparatus of claim 31, wherein the transport member mover is an endlessloop.
 33. The apparatus of claim 32, wherein the endless loop is a belt.34. The apparatus of claim 32, wherein the endless loop is a cable. 35.The apparatus of claim 31, further including a support structure, theinfeed and outfeed conveyors being mounted to the support structure, thetrack being mounted to the support structure and located at leastpartially in the space between the infeed and outfeed conveyors.
 36. Theapparatus of claim 35, further including guide members mounted to thesupport structure for guiding the transport member mover.
 37. Theapparatus of claim 35, wherein the guide members include one of pulleysor idler rollers.
 38. The apparatus of claim 31, wherein thedifferential drive mechanism drives the transport member mover at aspeed equal to half the difference between the speeds of the infeed andoutfeed conveyors.
 39. The apparatus of claim 31, wherein thedifferential drive mechanism drives the transport member mover at aspeed proportional to as₁−bs₂, where s₁ is the speed of the infeedconveyor and s₂ is the speed of the outfeed conveyor, and a and b areadjustable parameters.
 40. The apparatus of claim 31, wherein the infeedand outfeed conveyors are configured to convey the articles in a firstin, first out sequence.
 41. The apparatus of claim 40, wherein theinfeed and outfeed conveyors are configured to convey the articles in asingle file orientation.
 42. The apparatus of claim 40, wherein theinfeed and outfeed conveyors are configured to convey the articles in agreater than single file orientation.